U.S. patent number 5,302,026 [Application Number 08/056,571] was granted by the patent office on 1994-04-12 for temperature probe with fast response time.
This patent grant is currently assigned to Rosemount, Inc.. Invention is credited to Richard W. Phillips.
United States Patent |
5,302,026 |
Phillips |
April 12, 1994 |
Temperature probe with fast response time
Abstract
A temperature probe measures the temperature of a fluid which
moves relative to the probe. The probe includes a housing, a
transducer, and one or more fins. The housing has a bore with a
bore axis and carries at least a portion of the fluid along the
bore axis. The transducer has a sensing length, and the fin
thermally couples to the transducer along substantially the entire
sensing length. The fin is also substantially aligned with the bore
axis to promote laminar flow of the fluid in the bore. In a
preferred embodiment the transducer is held within a protective
tube, and the fin attaches to the tube along a fin inner edge. The
fin also attaches along a fin outer edge to a radiation shield
encircling the tube, the fin outer edge being shorter than the fin
inner edge.
Inventors: |
Phillips; Richard W. (Eagan,
MN) |
Assignee: |
Rosemount, Inc. (Inver Grove
Heights, MN)
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Family
ID: |
25435087 |
Appl.
No.: |
08/056,571 |
Filed: |
April 29, 1993 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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915016 |
Jul 16, 1992 |
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Current U.S.
Class: |
374/135; 374/138;
374/148; 374/E13.006 |
Current CPC
Class: |
G01K
13/028 (20130101); G01K 13/02 (20130101) |
Current International
Class: |
G01K
13/00 (20060101); G01K 13/02 (20060101); G01K
013/02 (); G01K 001/16 (); G01K 001/18 () |
Field of
Search: |
;374/135,138,148 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0128318 |
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Jul 1985 |
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JP |
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0080021 |
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Apr 1986 |
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JP |
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0091532 |
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May 1986 |
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JP |
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0234709 |
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Jan 1969 |
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SU |
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0616009 |
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Jan 1949 |
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GB |
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0788319 |
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Dec 1957 |
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GB |
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Other References
A Hill; NASA Tech. Briefs, MFS 29199, Feb. 1988; Mechanics
Hardware, Techniques, and Processes; Vortex Suppressors Reduce
Probe Vibrations. .
Max Jakob; Copyright 1949 (Printed May 1962); Heat Transfer; pp.
217, 218, 229, 230, and 231. .
Design News, Design Cuts Sensor's Response Time; Charles J. Murray;
pp. 176-177. (Mar. 25, 1991). .
Two Sheets with Figs. (A)-(D) showing views of temperature probe
subassembly types; Manufactured and sold by Rosemount Inc. (No
Date)..
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Primary Examiner: Cuchlinski, Jr.; William A.
Assistant Examiner: Gutierrez; Diego F. F.
Attorney, Agent or Firm: Westman, Chaplin & Kelly
Parent Case Text
This is a continuation of application Ser. No. 07/915,016 filed on
Jul. 16, 1992, now abandoned.
Claims
What is claimed is:
1. A probe for measuring a temperature of a fluid moving relative
to the probe, comprising:
a housing having a bore with a bore axis, the housing adapted to
carry at least a portion of the fluid along the bore axis;
a transducer having a thermally responsive characteristic, the
transducer further having a sensing length; and
at least one fin disposed in the bore and thermally coupled to the
transducer along substantially the full sensing length;
wherein the fin is thermally coupled to the transducer to a greater
extent than any thermal coupling between the fin and the housing,
and the fin is substantially aligned with the bore axis to promote
laminar flow of the fluid.
2. The probe as recited in claim 1, further comprising:
a tube disposed in the bore and thermally communicating with the
fin and the transducer, the transducer being disposed in the
tube.
3. The probe as recited in claim 2, wherein the fin attaches to the
tube along a fin inner edge.
4. The probe as recited in claim 3, wherein the fin has a trailing
fin edge, and wherein at least a portion of the trailing fin edge
is tapered at an acute angle to the fin inner edge.
5. The probe as recited in claim 1, the fin comprising a
substantially planar copper member with a coating of
corrosion-resistant material.
6. A probe for measuring a temperature of a fluid moving relative
to the probe, comprising:
a housing having a bore with a bore axis, the housing adapted to
carry at least a portion of the fluid along the bore axis;
a transducer having a thermally responsive characteristic, the
transducer further having a sensing length; and
a plurality of fins disposed in the bore and thermally coupled to
the transducer along substantially the full sensing length;
wherein the fins are thermally coupled to the transducer to a
greater extent than any thermal coupling between the fins and the
housing, and the fins are substantially aligned with the bore axis
to promote laminar flow of the fluid.
7. The probe as recited in claim 6, further comprising:
a tube disposed in the bore and thermally communicating with the
fins and the transducer, the transducer being disposed in the
tube.
8. The probe as recited in claim 7, wherein the thermal coupling of
each fin to the transducer is achieved by attachment of each fin to
the tube along a fin inner edge.
9. The probe as recited in claim 8, further comprising an
open-ended member disposed in the bore, the open-ended member
encircling the tube and the fins.
10. The probe as recited in claim 9, wherein each fin attaches to
the open-ended member along a fin outer edge, and wherein the fin
outer edge is shorter than the fin inner edge.
11. The probe as recited in any one of claims 1, 6, or 10, further
comprising:
system means for detecting the thermally responsive characteristic
to provide an output as a function thereof; and
display means for displaying the output.
12. The probe as recited in either of claims 1 or 6, wherein the
transducer comprises a wound length of platinum wire.
13. The probe as recited in either of claims 1 or 6, wherein the
transducer comprises a quantity of luminescent material.
14. A probe for measuring a temperature of a fluid moving relative
to the probe, comprising:
a housing having a bore with a bore axis, the housing adapted to
carry at least a portion of the fluid along the bore axis;
a transducer disposed in the bore and having a thermally responsive
characteristic, the transducer further having a sensing length;
and
at least one fin disposed in the bore and mechanically coupled to
the transducer by an inner edge of the fin along substantially the
full sensing length;
wherein at least a portion of an outer edge of the fin is spaced
apart from the housing to reduce conductive heat transfer
therebetween and the fin is substantially aligned with the bore
axis to promote laminar flow of the fluid.
Description
BACKGROUND OF THE INVENTION
This invention relates to temperature probes, and in particular to
those temperature probes which measure the temperature of a fluid
moving relative to the probe.
BRIEF SUMMARY OF THE INVENTION
In the present invention, a temperature probe includes one or more
fins thermally coupled to a transducer along substantially a full
sensing length of the transducer. The fin or fins are disposed to
enhance convective heat transfer between the transducer and a fluid
moving relative to the probe, and to promote laminar flow of the
fluid. The probe further includes a housing having a bore with a
bore axis, the housing carrying at least a portion of the fluid
along the bore axis. The fins are disposed in the bore, and in a
preferred embodiment attach to a tube in which the transducer is
located. The fins enhance the convective heat transfer by
increasing an effective surface area-to-mass of the transducer,
thereby quickening a response time of the transducer to a transient
flow condition. In a preferred embodiment, the fin attaches to the
tube along a fin inner edge and has a trailing fin edge which
tapers at an acute angle to the fin inner edge.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view partly broken away and sectioned
of a temperature probe in accordance with the invention;
FIG. 2 is a perspective view partly broken away of a temperature
probe subassembly taken from FIG. 1;
FIG. 3 is a side elevational view partly broken away and sectioned
of a portion of an alternate embodiment of a temperature probe
subassembly in accordance with the invention;
FIG. 4 is an end view taken along line 4--4 of FIG. 2;
FIG. 5 is an end view taken along line 5--5 of FIG. 3; and
FIG. 6 is a view of an alternate embodiment of the temperature
probe of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1, temperature probe 10 measures the temperature of a fluid
shown generally at 12. Preferably, probe 10 mounts on an air
vehicle and measures total air temperature. Probe 10 includes a
housing 14, which has a bore 16 of a generally cylindrical shape
and aligned along a bore axis 18,18. The fluid enters opening 20 in
housing 14, and at least a portion of the fluid generally follows
arrow 22 into bore 16. Another portion of the fluid, along with
debris including water droplets, if present, passes through the
housing via cavity 24. Still other portions of the fluid flow
through holes 26 to reduce undesirable boundary layer effects. This
and other aspects of preferred housings for use with the present
invention are taught in U.S. Pat. No. 2,970,475, which is
incorporated herein by reference.
Fluid 12 undergoes adiabatic heating when its speed is reduced by
housing 14. The heated fluid flows at least partially into bore 16
along bore axis 18, encountering a probe subassembly 50 which
includes fins 28 thermally coupled to a transducer 30. Probe
subassembly 50 also preferably includes a tube 32 and a radiation
shield 34. In ruggedized embodiments of the invention, transducer
30 is preferably housed in tube 32 which is closed to protect the
transducer against corrosion and other harmful influences. Some of
the heated fluid flows inside radiation shield 34, an open-ended
member, coming into contact with fins 28 and tube 32. This fluid
then passes through holes 36 in a lower portion of the probe
subassembly, through holes 38 in bore 16 and exits probe 10 via
holes 40. Other portions of the heated fluid flow between radiation
shield 34 and bore wall 17, passing through holes 38 and exiting
probe 10 Via holes 40.
According to the invention, the fluid transfers heat to transducer
30 not only directly or through tube 32, but also via fins 28. Fins
28, in effect, increase an effective surface area of transducer 30
exposed to the fluid flow, thereby enhancing thermal coupling of
the transducer to the fluid. This enhanced thermal coupling
improves the time response of the transducer and reduces errors due
to competing thermal effects such as stem conduction or radiation
heat transfer.
Fins 28 are preferably composed of a high thermal conductivity
material such as copper, and are thermally coupled to transducer 30
along substantially an entire sensing length L of transducer 30
(see FIG. 2). If composed of copper, fins 28 also preferably
include a thin coating of a corrosion-resistant material such as
nickel to prevent degradation of the copper. Fins 28 are also
sufficiently thin so that the effect on the probe of the additional
fin mass (tending to slacken the probe time response) is smaller
than the effect of the additional fin surface area (tending to
quicken the probe time response) to yield a net quickening of the
probe time response to changes in fluid temperature. Fins 28
preferably have a substantially planar shape and are aligned with
bore axis 18 for reasons discussed below.
FIG. 2 shows enlarged the temperature probe subassembly 50 from
FIG. 1. Although each fin 28 contacts the fluid along an entire
length of the fin, heat transfer from the fluid to the fin and vice
versa occurs predominantly at a leading fin edge 28a of each fin.
Comparatively little such heat transfer occurs at a trailing fin
edge 28b. For this reason, trailing fin edge 28b is preferably
tapered at an acute angle relative to a fin inner edge 28c, along
which fin 28 attaches to tube 32. Such tapering permits reduced fin
mass but retains heat conduction from leading fin edge 28a through
fin 28 to transducer 30 along substantially its entire length L.
Attachment of fin 28 to tube 32 is preferably by a braze or weld
joint for ruggedness.
Transducer 30 has a thermally responsive characteristic and a
sensing length L. Preferably, transducer 30 is a resistance
temperature device (RTD) comprising a length of platinum wire wound
around a cylinder of high resistivity material such as aluminum
oxide. In such case, the thermally responsive characteristic is the
electrical resistance of the RTD, and probe 10 includes wires 31
connecting transducer 30 over line 44 to a circuit means 42 for
measuring the resistance of the RTD and providing an output 46 as a
function thereof. Output 46, indicative of the temperature of fluid
within bore 16, can be used in a closed-loop control system or
displayed on an indicator 48. In other embodiments, such as in FIG.
6, transducer 30a comprises other known temperature transducers
such as a thermocouple or a quantity of luminescent material.
Temperature probe 10 also preferably includes radiation shield 34
encircling tube 32 and fins 28. Fluid flowing along inside and
outside surfaces of radiation shield 34 heats or cools it in like
manner to fins 28, tube 32, and ultimately transducer 30. In some
circumstances shield 34 attains temperatures which, although close
enough to the temperature of transducer 30 to act as an effective
radiant heat shield, may deviate from the transducer
temperature.
Fins 28 preferably attach to radiation shield 34 at fin outer edges
28d to secure transducer 30 against vibration. Fins 28 thus serve a
dual purpose: they enhance thermal coupling of transducer 30 to the
fluid, and they also provide mechanical support for transducer 30.
Fin outer edges 28d are as short as practical, preferably much
shorter than edges 28c, to reduce conductive heat transfer between
transducer 30 and shield 34, thereby to make the transducer
temperature more representative of the fluid temperature. Keeping
fin outer edges 28d short also reduces the effective thermal mass
of the transducer, thereby enhancing time response. In alternate
embodiments, some or all of the fins can remain unattached to the
heat shield to further reduce conductive heat transfer between the
transducer and the radiation shield.
According to the invention, fins 28 are substantially aligned with
bore axis is to promote laminar fluid flow rather than turbulent or
swirling fluid flow. Turbulent fluid flow in the region between
transducer 30 and radiation shield 34 is undesirable because it can
increase thermal coupling between transducer 30 and shield 34 by
convection of fluid portions between those members. Such increased
coupling is undesirable because of temperature differences between
the members as discussed above.
FIG. 4 shows a view of probe subassembly 50 along line 4--4 of FIG.
2. The three fins 28, tube 32, radiation shield 34, and multiple
holes 36 are clearly seen. Holes 36 can be circular in
cross-section, as shown in FIG. 4, or they can have non-circular
cross sections.
FIG. 3 shows an alternate embodiment of a temperature probe
subassembly 60 similar to the subassembly of FIG. 2. Probe
subassembly 60 comprises fins 62 thermally coupled to a transducer
64 along its entire length L', as well as protective tube 66 and
radiation shield 68. Fins 62 preferably attach to tube 66 along fin
inner edges 62a and to radiation shield 68 along fin outer edges
62b by a braze or weld joint. As in the previous embodiment,
trailing fin edges 62c taper at an acute angle relative to fin
inner edges 62a. Subassembly 60, like subassembly 50, fits within a
bore of a temperature probe housing such that fins 62 align with an
axis of the bore. FIG. 5 shows a view of temperature probe
subassembly 60 along line 5--5 of FIG. 3. The four fins 62 and
neighboring members are clearly seen. Temperature probes according
to the invention can of course have other numbers of fins, such as
one, two, or more. An excessive number of fins can increase the
cost of manufacturing the temperature probe, and placement of fins
too close together, such that fluid boundary layers from surfaces
of adjacent fins meet or touch, are not preferred.
The present invention has been described with reference to
preferred embodiments. Workers skilled in the art, however, will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *